Hungry fungi chomp on radiation

May 23, 2007By Heidi LedfordThis article courtesy of Nature News.

Common pigment may allow bizarre feeding habits.

From plastic to asbestos, cardboard to jet fuel, fungi will eat just about anything. Now researchers have found another dish
in the fungal diet: radiation. Not radioactive compounds, which have long been known to be on the menu — radiation itself.

Ekaterina Dadachova and her colleagues at the Albert Einstein College of Medicine in New York have discovered that some fungi
can use a molecule called melanin, a pigment also found in human skin, to harvest the energy from radiation and use it for
growth.

This raises the prospect that astronauts could grow these fungi on long flights into radiation-rich outer space, suggests
Dadachova's colleague Arturo Casadevall. The fungi aren't particularly appetizing, however — they resemble the mould on a
dirty shower curtain.

Since the 1986 meltdown, at the Chernobyl Atomic Energy Station, the numbers of 'black fungi', rich in melanin, have risen
steeply. Casadevall speculated that the fungi could be feeding on the radiation that contaminates the ruin of the nuclear
reactor.

Dadachova, Casadevall and their colleagues tested how three different species of fungus respond to beta-radiation from caesium-137,
which is produced during nuclear fission of uranium and plutonium. They found that all three, Cladosporium sphaerospermum, Cryptococcus neoformans and Wangiella dermatitidis, grow faster in the isotope's presence. The results are published in PLoS One.1

Heat seekers

Some fungi can decompose radioactive material such as the hot graphite in the remains of the Chernobyl reactor. Previous studies
have shown that most fungi found in contaminated regions grow towards various different radiation sources, as if trying to
reach these compounds2.

These fungi also tend to produce the pigment melanin, which is thought to protect fungi from a range of environmental stresses.
"Under stress of exposure to ionizing radiation, microfungal communities in soil develop a higher proportion of melanin-containing
fungal species," says John Dighton, a microbiologist at Rutgers University in New Brunswick, New Jersey.

Dadachova's team found that exposure to radiation caused the fungal melanin molecule to change shape so that it was four times
better at carrying out a common metabolic chemical reaction. Fungal strains without melanin generally did not grow faster
in response to radiation.

Could the melanin in human skin cells likewise turn radiation into food? Casadevall speculates that it might, but the amount
of energy provided would probably be very small — and certainly not enough for a busy astronaut. "Currently there is no evidence
for this," says Casadevall, "however the fact that it occurs in fungi raises the possibility that the same may occur in animals
and plants."